1. Field of the Invention
The present invention relates to a bonding pad and a chip structure. More particularly, the present invention relates to a bonding pad having different geometric shapes and a chip structure.
2. Description of the Related Art
In the recent decade, electronic technologies have been progressing at a tremendous pace, especially in the technique of fabricating integrated circuits (IC). Electronic devices having multiple functions are produced at an ever-decreasing cost.
In general, semiconductor fabrication can be roughly divided into a front stage and a back stage. The front stage processing includes mask fabrication, oxidation, photolithography, etching, deposition and doping. To establish input/output communication channels between a chip and an external device, bumps are often formed on the input/output bonding pads of a chip.
FIG. 1 is a schematic cross-sectional view of a conventional chip structure. As shown in FIG. 1, the chip structure 100 comprises a chip 120, a bonding pad 140, a bump 180 and a passivation layer 160. The bonding pad 140 is disposed on an active surface 122 of the chip 120 for inputting/outputting signal. The passivation layer 160 is disposed on the active surface 122 but has an opening that exposes the bonding pad 140. The bump 180 is disposed on and electrically connected to the bonding pad 140.
FIG. 2 is a perspective view of the bonding pad in FIG. 1. As shown in FIGS. 1 and 2, the bonding pad 140 has a flat rectangular shape. Using the driving chip of a liquid crystal display as an example, the driving chip is normally bonded to the glass substrate (not shown) of a liquid crystal display by thermal compression. In the process of bonding the chip 120 to the glass substrate through thermal compression, thermal stress are often created between the bumps 180, the bonding pads 140 and the passivation layer 160 due to differences in their coefficient of thermal expansion (CTE). The corner regions of the bonding pads 140 are particularly vulnerable to stress concentration effects.
Therefore, the electrical connection between the bump 180 and the bonding pad 140 is easily damage around the corner region of the bonding pads 140 when the flat top surface of the bonding pad 140 is made to contact the passivation layer 160 and the bump 180. Since the bonding pads 140 are used for transmitting signals into and out of the chip 120, any damage in the electrical connection between the bump 180 and the bonding pad 140 will lead to a drop in the reliability of the entire electronic product. In addition, if the passivation layer 122 cracks under the effect of thermal stress, moisture can easily migrate into the chip 120 to cause possible damages. Hence, it is important to reduce the damage to the chip package 100 due to thermal stress.